1. Technical Field of the Invention
The present invention relates generally to an engine control system which may be employed in automotive vehicles and is designed to use an algorithm to control operations of actuators such as a fuel injector and an EGR (Exhaust Gas Recirculation) valve to regulate a combustion condition of fuel in an internal combustion engine and also to control output characteristics of the engine.
2. Background Art
Engine control systems are known which determine controlled variables such as the quantity of fuel to be injected into an engine (which will also be referred to as an injection quantity), the injection timing, the amount of a portion of exhaust gas to be returned back to the inlet of the engine (which will also be referred to as an EGR amount below), the boost pressure (also called supercharging pressure), the amount of intake air, the ignition timing, and an open/close timing of intake and exhaust valves to bring engine output-related values such as the amount of exhaust emissions, for example, NOx or CO, the torque outputted by the engine, and the specific fuel consumption (or fuel efficiency) into agreement with required values.
For example, Japanese Patent First Publication Nos. 2008-223643 and 2007-77935 disclose the above type of engine control systems which calculate a target value of pressure in a cylinder of the engine (i.e., a combustion parameter) based on a value of torque the engine is required to output and adjust the open/close timing of the intake and exhaust valves and the quantity of fuel to be injected into the engine (i.e., controlled variables of actuators) so as to bring the in-cylinder pressure into agreement with the target value.
The above engine control systems have the drawback in that correlations between the engine output-related values and the controlled values usually change with a change in environmental is condition such as the temperature of outside air or due to an individual variability of the engine, which will result in deviations between the engine output-related values from the required values.
The problem may be eliminated by learning changes in correlations between the engine output-related values and the controlled variables depending upon the change in environmental condition. This, however, requires the measurement of emissions from the engine such as NOx or PM, the output torque from the engine, the fuel consumption in the engine, or noises arising from combustion of fuel in the engine (i.e., the engine output-related values), thus resulting in a great increase in cost to install the system in automotive vehicles. In order to alleviate this problem, some of the engine control systems are designed to correct the correlations between the engine output-related values and the controlled variables so as to compensate for changes therein with a change in environmental condition of the engine using a correction map or learning only the correlations associated with the measurable engine output-related values. The making of the correction map requires lots of data on correspondence between the engine output-related values and the controlled variables under environmental conditions that the correlations are needed to be corrected, thus imposing a heavy burden on control system manufacturers or resulting in possibility of a difficulty in bringing all the engine output-related values into agreement with required values thereof.
Moreover, some of the engine output-related values can be measured using vehicle-installed sensors directly (e.g., the measurement of NOx using a NOx sensor) or indirectly (e.g., the measurement of PM using an A/F sensor) in order to learning the correlations between the engine output-related values and the controlled variables partially, however, the problem is encountered in that when the responsiveness of the sensors is low undesirably, the partial learning needs to be made only in a limited condition, for example, where the engine is running in the steady state.